Systems or devices wherein light (i.e., select forms/wavelengths of electromagnetic energy) is an important consideration, factor, or “input” in furtherance of system or device functionality, or wherein a “view” through a system or device “window” for an assessment of local/distant objects and/or surroundings is essential to system or device function or performance, are well known. Exemplary applications include, but are hardly limited to, imaging systems such as optoelectronic (e.g., U.S. Pat. Appl. Pub. No. US 2006/0060802 A1 (Richter et al.)) and/or biometric (e.g., U.S. Pat. Nos. 6,809,303 B2 (Carver et al.) and 5,825,474 (Maase)), optical scanners/scanning such as bar code readers or the like (e.g., U.S. Pat. Nos. 6,612,493 B2 (DeGiovine et al.) and 5,729,003 (Briggs, III)), light emitting diode (LED) fixtures such as vehicle headlamps (e.g., U.S. Pat. No. 6,601,983 B1 (Runfola et al.)) and/or traffic control signal lights (e.g., U.S. Pat. No. 7,211,771 B1 (Smith et al.)), liquid crystal display (LCD) screens (e.g., U.S. Pat. Nos. 6,727,468 B1 (Nemeth) and 7,023,519 B2 (Ho et al.)), cameras/telescopes/sights/range-finders (e.g., U.S. Pat. No. 6,866,391 B2 (Krausse)), and/or self guided munitions, vehicles, etc.
Whether owing to natural environmental conditions (e.g., ambient atmospheric conditions with regard to use of a telescope, camera, munition guidance system, etc.) or artificial environmental conditions part and parcel of a manufacturing or industrial processes/processing (e.g., refrigerated systems wherein optical scanning is conducted or processes wherein LCD instrumentation is present), optical interference via the formation of condensate and/or ice, whether water vapor or other saturated gaseous element/compound associated with a given process/application, often times renders such systems or devices inoperative, and if not, nonetheless greatly alters system/device performance. Among the heretofore known, well documented approaches to avoid/remedy such diminished capacity, the thermal conditioning of such optical lens, electro-optical system, “windows,” etc. appears favored and widely practiced.
One current method to provide thermal energy to an optical lens or window is to apply a resistive heater to its perimeter, leaving the center completely unobstructed (see e.g., Carver et al. '303 FIGS. 5 & 6). This approach relies on thermal energy conducting laterally through the optical lens or window material to provide sufficient heating in the center of the component. Due to the poor thermal-conduction properties of typical optical materials, a large temperature gradient occurs between the heated perimeter and the center of the lens/window. As a result, such approaches are characterized by a loss of efficiency as a “high” perimeter temperature must be maintained in order to provide sufficient heat at the center of the component to maintain or support the sought after optical effect.
Another current method to provide thermal energy to an optical lens or window is to apply a sheet, panel, or laminate of “clear” adhesive film to one surface of the optical component (see e.g., Briggs, III '003). Such films generally support a fine resistive wire, commonly by embedding or otherwise “capturing” the wire between layers thereof, or upon a layer surface, so as to form a resistive heating element or article (i.e., a fixation medium such as film “carries” a selectively configured resistive wire). The resistive wire can be located within or with respect to the film so as to selectively correspond/register with portions of the optical/transparent substrate (e.g., lens/window, etc.) where it is intended to provide optimal condensation/ice control. This method provides excellent thermal efficiency, however, as the adhesive film article overlies the entirety of the optical component, as “clear” as the film article may be, it nonetheless degrades the clarity of the lens/window (i.e., the application of the film increases the opacity of the lens/window), often times resulting in an unacceptable optical distortion.
A further current method to provide thermal energy to an optical lens or window is to apply a very thin coating/deposition of metal film, e.g., indium tin oxide (ITO), upon a substrate, e.g., polyester sheet or the like (see e.g., Ho et al. '519). In connection with such depositions, printed ink bus bars generally link the deposited metal film with crimped or adhesively bonded lead connections which extend from at least one bus bar end, and commonly both opposing bus bar ends. While this method or approach arguably provides improved optical performance in connection to transmittance and/or reflectance, thermal performance is generally less robust than that associated with adhesive film, and lead connections are generally believed less reliable than those associated with wire-element heaters.
For the most part, the latter film approaches, namely wire-element heating structures and thin-film coatings/depositions, have become the norm across most application fields, with each discussed and compared in a publication entitled “Comparison of Thin-film and Wire-element Heaters for Transparent Applications,” Application Aid #30, Jul. 31, 2001, Minco Products, Inc., Minneapolis, Minn., incorporated herein by reference in its entirety. In as much as there no doubt are application criteria that support the selection of one heater style over the other, e.g., ITO film heaters provide an uninterrupted visible area, i.e., no shadows or light disruptions, whereas wire-element film heaters deliver more uniform heat flux and generally possess tighter resistance tolerances, with regard to heretofore known wire-element approaches, improvements in the area of light transmission are believed particularly advantageous and remain outstanding. Arguably, an improved thermally conditionable light transmitting subassembly would be characterized by an amalgamation of the advantageous features of each of the heretofore known approaches while if not eliminating, reducing the shortcomings of each.
In light of the foregoing, it is believed advantageous and desirable to provide a wire-element heater for transparent applications which possess a clarity/light transmittance on par with that presently available/associated with heretofore known thin film heaters while nonetheless offering: a greater range of electrical resistance; greater flexibility in profiling the resistance density across a surface/substrate; greater reliability due to the stability and durability associated with a solid/traditional wire; reliable and durable lead connections or the ability to obtain same; and, the ability to manufacture to tighter resistance tolerances in furtherance of reducing power consumption. Further still, it is believed advantageous and desirable to avoid thermal elements characterized by a laminate or substrate overlay for the prevention or remedying of condensate/ice formation on optical components/windows or the like. More particularly, it is believed especially advantageous to directly mate, as by bonding or the like, a thermal element in the form of a resistive wire to a light transmissive substrate in furtherance of providing greater clarity and/or light transmittance in excess of about 90%.
Thus, in furtherance of maintaining or restoring the optical integrity of articles and/or systems possessing a lens/window, it is believed advantageous to eliminate the heretofore known coextensive or substantially coextensive wire-element retaining media of adhesive films which overlie a lens/window (i.e., more generally a transparent substrate), while nonetheless retaining such precise and efficient heating of such heating structures.